Why does du/dT = Cv, and same for Cp? Also, i dont understand how Cp/Cv = v, where v is the specific volume. It is derived from: Cv + R = Cp, how is PV=nRT used to get from Cv + R = Cp to Cp/Cv = v? I know n is replaced by m/M to leave Pv=RT where R would equal R(universal gas const)/M, but how would you use that? If anyone could please explain any of these things to me i would really appreciate it. This is for a 1st year mech eng undergraduate who has his thermo exam in just over 2 weeks!!. cheers.